1. Field of the Invention
The present invention relates to acoustic devices including an acoustic lens, an ultrasonic delay line and an acoustic optical deflecting device.
2. Description of the Related Art
An acoustic lens is employed as a probe of a non-destructive testing device such as an ultrasonic microscope. The focal distance of the acoustic lens is substantially constant. If an acoustic lens capable of changing its focal distance is employed in this type of device, that is very convenient, and there is a great demand for such an acoustic lens. To meet the demand, an acoustic lens has been proposed, wherein a plurality of oscillators such as piezoelectric elements are arranged concentrically, and a driving voltage is applied to the oscillators successively from the outer ones toward the central ones with slight time lags, thereby generating convergent acoustic waves. The generated acoustic waves, however, are not acoustic waves obtained by converging plane waves, but are convergent acoustic waves obtained by superimposing a plurality of acoustic waves. Consequently, there is a problem that, owing to diffraction of respective acoustic waves from each oscillator, wave fronts, or phases, do not coincide.
An ultrasonic delay line comprises an acoustic wave propagating medium having an incidence face and an emission face. A time required until an incident ultrasonic wave incident on the incidence face is emitted from the emission face, i.e. a delay time, is determined by the shape of the acoustic wave propagating medium and acoustic velocity. An ultrasonic delay line capable of changing the delay time continuously has not yet been proposed.
In an acoustic optical deflecting device, a phase grating is produced within an acoustic wave propagating medium by ultrasonic waves. Utilizing optical diffraction by means of the phase grating, light is deflected. The response speed of the acoustic optical deflecting device is very excellent, compared to a mechanical optical deflector such as a polygonal mirror or a galvanomirror. Thus, this device has been regarded as very useful in the field of recent image processing or optical communication which require high-speed operations; however, a high deflecting angle is not obtained. In other words, a deflection efficiency is low. Under the situation, there is a demand for an acoustic optical deflecting device with high deflection efficiency.